From fc066992d912186da08ac9250b3772103aafbbe8 Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Tue, 17 Jan 2023 20:06:41 +0200
Subject: [PATCH] Sema: do not create slices with undefined pointers

The undef pointer ended up being zero on wasm32.
---
 src/Sema.zig | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index 943f0adf6b..dcc38e4c0a 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -24822,8 +24822,13 @@ fn coerceExtra(
                     // empty tuple to zero-length slice
                     // note that this allows coercing to a mutable slice.
                     if (inst_child_ty.structFieldCount() == 0) {
+                        // Optional slice is represented with a null pointer so
+                        // we use a dummy pointer value with the required alignment.
                         const slice_val = try Value.Tag.slice.create(sema.arena, .{
-                            .ptr = Value.undef,
+                            .ptr = if (dest_info.@"align" != 0)
+                                try Value.Tag.int_u64.create(sema.arena, dest_info.@"align")
+                            else
+                                try inst_child_ty.lazyAbiAlignment(target, sema.arena),
                             .len = Value.zero,
                         });
                         return sema.addConstant(dest_ty, slice_val);